The present invention relates to a method of forming a high precision hermetic seal by axially inserting a spherical lens into a cylindrical opening in a metal body, wherein the spherical lens has a larger diameter than the cylindrical opening.
When coupling a light waveguide to another optical component, merely placing the end face of the waveguide as close as possible to the other optical component may nevertheless attenuate the light at the coupling. It is often better to insert a spherical lens between the end of the waveguide and the optical component because the spherical lens can cause less attenuation of the light in the coupling.
It is often important in the foregoing coupling to locate at least one of the elements in a hermetically sealed space. The hermetic seal prevents the component from coming in contact with undesirable influences such as moisture. For example, if a light waveguide is coupled to a light emitting diode (LED), the LED needs to be well protected. It follows that a spherical lens that is located between the light emitting diode and the end face of the fiber of the wave guide should form a hermetic seal with the wall of the housing to thus enclose the light emitting diode.
European Patent Application EP A2 0,191,328, corresponding to U.S. Pat. No. 4,726,648, shows a hermetically sealed fitting for a lens. This application describes a spherical lens that is intergrown with a ring so that the ring folds over the lens to form a hermetic seal around the circumference of the spherical lens. The ring is inserted and hermetically sealed to the wall of the housing. The housing contains a photo diode or a laser diode that is coupled to a light waveguide via the inserted lens. Providing hermetic seals at both the lens and the housing, however, is expensive.
Another way to seal a lens into a housing wall is described in U.S. Pat. No. 3,950,075. This patent discloses inserting a glass lens into a plastic ring that has an inside diameter that is smaller than the outside diameter of the lens. The lens deforms the ring so that the elasticity of the ring material forms a hermetic seal. However, it has been found that the long term stabilitY of the tightness of this connection is unsatisfactory.
European Patent Application EP A 0,256,892 describes a hybrid plug for a connector in which spherical lenses are axially pressed into the openings of a metallic body. Experience has shown, however, that fastening a spherical lens with a press fit does not always form a hermetic seal. The seal leaks in response to temperature fluctuations because the material of the spherical lens and the metal have different coefficients of expansion for different temperatures.
There is a need to fit a lens into a metallic housing wall to form a hermetic seal. The tightness of the sealed fit o needs to be reliable over the long term without incurring unjustifiable manufacturing costs.